Ruxolitinib for rheumatic disease-associated macrophage activation syndrome in children: a retrospective cohort study.

Objective: Macrophage activation syndrome (MAS) is a severe, life-threatening complication in pediatric rheumatic diseases. Current treatments are predominantly based on glucocorticoids; however, their long-term use is associated with significant adverse effects. Ruxolitinib, a Janus kinase (JAK) inhibitor, has emerged as a potential treatment option, but clinical evidence in pediatric populations remains limited. This study aimed to evaluate its efficacy and safety in pediatric patients with rheumatic disease-associated MAS (RD-MAS). Methods: We retrospectively reviewed the medical records of pediatric patients with RD-MAS treated at Shenzhen Children's Hospital between January 2021 and December 2025. Eligible patients had a confirmed rheumatic disease, fulfilled the 2016 EULAR/ACR classification criteria for MAS, and had complete clinical, laboratory, treatment, and follow-up data. Patients who received ruxolitinib in addition to conventional immunosuppressive therapy were compared with contemporaneous patients treated with conventional immunosuppressive therapy alone. The primary outcome was time to complete remission (CR). Secondary outcomes included remission rates during follow-up, changes in laboratory parameters, glucocorticoid-sparing effect, cumulative glucocorticoid exposure, and adverse events. Results: A total of 21 patients with RD-MAS were included, of whom 10 received ruxolitinib (ruxolitinib group) and 11 received conventional therapy alone (non-ruxolitinib group). In the ruxolitinib group, 10 patients (6 males, 4 females) had underlying diagnoses of systemic juvenile idiopathic arthritis (sJIA, n = 7), systemic lupus erythematosus (SLE, n = 1), or other connective tissue diseases (n = 2). All patients presented with active disease at baseline. 30% (3/10) of patients achieved CR by week 4, and all patients achieved CR by week 48. By week 8, the median prednisone-equivalent dose decreased from 4 mg/kg/day to 0.4 mg/kg/day, and all patients successfully discontinued glucocorticoids by week 48 while maintaining remission. No significant difference in time to CR or infection rates was observed between groups. However, the ruxolitinib group demonstrated significantly lower cumulative glucocorticoid exposure during follow-up. Conclusions: Ruxolitinib-based therapy was associated with sustained disease control and a significant glucocorticoid-sparing effect in pediatric RD-MAS. These findings support that ruxolitinib may serve as a promising steroid-sparing strategy with favorable efficacy and safety for pediatric RD-MAS, although larger prospective studies are warranted.